Torque sensor

ABSTRACT

A torque sensor generates an electric signal representing a change in the state of electromagnetic or electrostatic coupling between first and second rotors coupled together by a torsion spring. The change is caused with relative rotation of the two rotors caused by detected torque in a power assisted steering system of an automotive vehicle.

BACKGROUND OF THE INVENTION

This invention relates to torque sensors and, more particularly, to atorque detector for a motor for providing assisting torque to a vehiclesteering shaft.

A method of detecting torque with a semiconductor strain gauge mountedon a steering main shaft has been contemplated. In this method, however,the output characteristics are subject to fluctuations with vibrationsof the semiconductor strain gauge or in long use. Also, problems arefound in the symmetricity of output characteristics with respect to thesame torques exerted on the opposite sides.

SUMMARY OF THE INVENTION

An object of the invention is to provide a torque sensor, which detecttorque through conversion of the relative rotation of first and secondrotors rotated relative to each other via a torsion bar by the detectedtorque converted into a corresponding electric signal.

Another object of the invention is to provide a torque sensor, whichcomprises a first rotor having a first coil supplied with a pulsevoltage signal, and a second rotor having a second coil perpendicularlyfacing the first coil at a predetermined distance therefrom, the secondrotor being coupled to the first rotor electrically by inductancecoupling and mechanically by a torsion spring, the positional relationbetween the first and second coils being caused due to a twist ordisplacement between the first and second rotors to change the magnitudeand direction of the magnetic flux crossing the seoond coil, the changebeing detected as a change in voltage and phase of a pulse voltagesignal produced across the second coil, thereby detecting the magnitudeand direction of torque exerted to a torsion spring causing the twist ordisplacement of the second coil with respect to the first coil.

A further object of the invention is to provide a torque sensor, whichcomprises a first rotor having two kinds of first electrodes suppliedwith respective signals of opposite phases, and a second rotor having asecond electrode facing the two kinds of first electrodes and coupledthereto electrically by electrostatic capacitance coupling andmechanically by a torsion spring, the area of overlap of each of the twofirst electrode and the second electrode being changed with a twist ordisplacement caused between the first and second rotors to cause greatchanges in the electrostatic capacitances of the individual electrodepairs, the change being detected as a change of the voltage signal fromthe second electrode, thereby detecting the magnitude and direction ofthe torque exerted to a torsion spring causing the twist or displacementof the second electrode with respect to the two kinds of firstelectrodes.

Use of comb-shaped electrodes as the first and second electrodes iseffective for increasing the precision of detection for small angles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a construction including a torquesensor embodying the invention.

FIG. 2 is a fragmentary sectional view showing the mechanical part of afirst embodiment of the torque sensor according to the invention.

FIGS. 3 and 4 are sectional views taken along lines III--III and IV--IVin FIG. 2.

FIG. 5 is a schematic showing an example of the electric circuit usedfor the embodiment of FIG. 2.

FIG. 6 is a waveform chart showing voltage waveforms appearing atvarious parts of the circuit of FIG. 5.

FIGS. 7A to 7C are schematic views showing respective status of thefirst and second coils for illustrating the operation of the firstembodiment.

FIG. 8 is a schematic view showing a second embodiment of the invention.

FIGS. 9 and 10 are sectional views taken along lines IX--IX and X--X inFIG. 8.

FIGS. 11 and 12 are plan views showing a specific example of the firstand second plates in the second embodiment of the invention.

FIG. 13 is a schematic showing an example of the electric circuit usedfor the embodiment of FIG. 8.

FIGS. 14A to 14C are schematic views showing respective status of theelectrodes for illustrating the operation of the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the invention will be described with reference tothe accompanying drawings. Referring now to FIG. 1, which outlines theentirety of the torque sensor according to the invention, a torquesensor 1 includes an electric circuit for detecting torque generated ina steering main shaft and generates a pulse duration signal proportionalto the detected torque. Designated at 2 is a steering wheel, at 3 thesterring main shaft, and at 4 and 5 gears meshing with each other.Torque assisting motor means 6 supplies motor torque proportional to thedetected torque represented by the signal from the torque sensor 1through the gears 4 and 5 to the main shaft 3. Designated at 7 aretires. The motor means 6 may include a motor drive circuit 6' forconverting the output signal from the sensor 1 into a motor controlsignal.

The motor drive circuit 6' may be arranged such that when the torquesensor 1 detects drive torque with the main shaft 3 driven in theclockwise direction, for instance, the motor 6 is driven to drive thetyres in the rightward direction. On the other hand, when drive torqueis detected with the main shaft driven by the steering wheel in thecounterclockwise direction, the motor 6 is driven in the oppositedirection to assist the driving of the tyres in the leftward direction.

FIG. 2 shows a fragmentary sectional view of the details of the internalconstruction of the torque sensor 1 shown in FIG. 2. A first rotor 11 issecured by a screw to a stay 12. A first bobbin 13 is secured by a screw14 to the stay 12. A first coil 15 is wound on the first bobbin 13. Asecond rotor 16 is secured by a screw 18 to a second bobbin 17containing ferrite (not shown). A second coil 19 is wound on the secondbobbin 17.

An electric circuit section 20 and a plate 21 having two slip rings tobe described later in detail are bonded by an epoxy adhesive to thefirst rotor 11. Brushes 24 and 25 are urged against the slip rings ofthe plate 21 by brush holders 26 and 27 comprising spring members sothat they are electrically connected to the slip rings even when thefirst rotor 11 is rotating, and they are secured by screws to bedescribed later to connector pins 28 and 29. The connector pins 28 and29 are bonded by epoxy resin to a connector holder 31. The connectorholder 31 has a holder cover to be described later, which is secured bya screw to a housing 33 to be described later.

A torsion bar spring 35 is pressure fitted in the first and secondrotors 11 and 16 and secured thereto by two knock pins 36. The first andsecond rotors 11 and 16 are coupled together via a bearing 37. The firstrotor 11 and housing 33 are coupled together via a bearing 38. The firstand second rotors 11 and 16 which are coupled together by the torsionspring 35, can thus be smoothly rotated with respect to the housing 33.

FIG. 3 is a section of the torque sensor 1 taken along line III--III inFIG. 2. In the Figure, designated at 33 is the housing, at 11 the firstrotor, and at 21 the plate, all these parts being as mentioned before.Designated at 22 and 23 are ring-like slip rings. The brush holders 26and 27 are secured by screws 30 to the respective connector pins 28 and29. A holder cover 32 of the connector holder 31 is secured by a screw34 to the housing 33.

FIG. 4 is a sectional view of the torque sensor taken along line IV--IVin FIG. 2. The stay a plate 12 is secured by screws 40 to the firstrotor 11, and is formed with holes 41, through which lead wires from thesecond coil 19 shown in FIG. 2 are led to the electric circuit 20.Designated at 13 is the first bobbin as mentioned, and at 15 the firstcoil as mentioned. The first rotor 11 is provided with a stopper 39 forpreventing the displacement of the first and second rotors 11 and 16relative to each other beyond a predetermined angle.

FIG. 5 is an electric circuit diagram showing the electric circuitry ofone embodiment of the torque sensor according to the invention, and FIG.6 is a waveform chart showing voltage waveforms appearing at variousparts of the circuitry. Referring to FIG. 5, shown at 51 is a batteryfor supplying power to the electric circuit 20. In series with thebattery 51 is a current detection resistor 52. A power supply terminal101 is connected through the slip ring 23, brush 25, brush holder 27 andconnector pin 29 shown in FIG. 3 to the resistor 52. A terminal 102 isconnected through the slip ring 22, brush 24, brush holder 26 andconnector pin 28 shown in FIG. 3 to the grounded terminal of the battery51. A terminal 103 is connected to one end of the second coil 19 woundon the second bobbin 17 shown in FIG. 2. The other end of the secondcoil 19 is connected to a terminal 105. A terminal 104 is connected toone end of the first coil 15 wound on the first bobbin shown in FIG. 4.The other end of the first coil 15 is connected to the terminal 105.

A constant voltage circuit 110, which includes a regulator 111 (whichmay be "MC7806" produced by Motorola INC. in U.S.A.) and capacitors 112and 113, always provides a constant output voltage. An initializingcircuit 120, which includes an inverter 121, a resistor 122 and acapacitor 123, generates a "1" level signal at the moment when power issupplied.

An oscillator 200, which includes an oscillating circuit havinginverters 201 and 202, a ceramic oscillator 203, a resistor 204 andcapacitors 205 and 206 as well as a binary counter 211 (which may be"TC4020" produced by Toshiba CORP.), inverters 212, 213 and 214, atransistor 215, resistors 216 and 217 and a diode 218, generates arectangular wave which is supplied via the terminal 104 to the firstcoil 15.

An amplifier 300, which includes an operational amplifier 301, resistors302, 303, 304, 305, 306 and 307 and capacitors 308 and 309, amplifies asignal produced from the second coil 19. A peak hold circuit 350, whichincludes an operational amplifier 351, resistors 352, 353 and 354, acapacitor 355 and a diode 356, holds the negative peak voltage of theoutput signal from the amplifier 300.

A triangle wave generator 400, which includes an operational amplifier401, resistors 402, 403 and 404 and a capacitor 405, generates atriangular wave. A left/right discriminating circuit 450, which includesD-type flip-flops 451 and 452 (which may be "TC4013" produced by ToshibaCORP.), operational amplifiers 453 and 454, an inverter 455, resistors456, 457, 458, 459, 460, 461 and 462 and capacitors 463 and 464,discriminates either lefward or rightward displacement of the secondcoil 19 with respect to the first coil 15.

A pulse duration converting circuit 500, which includes an operationalamplifier 501 and resistors 502, 503 and 504, generates a pulse durationsignal proportional to a voltage generated in the peak hold circuit 350.

A current value converting circuit 550, which includes NAND gates 551and 552, an inverter 553, transistors 555 and 556 and resistors 557,558, 559 and 560, converts the signals produced from the left/rightdiscriminating circuit 450 and pulse duration converting circuit 500into corresponding current value changes. More particularly, thiscircuit transmits information about the extent of leftward or rightwarddisplacement of the second coil 19 with respect to the first coil 15, inthe form of current value changes, to the power supply terminal 101.This information is detected as voltage changes at one end 53 of theresistor 52.

The operation of the construction described above will now be described.A pulse signal generated from the inverter 202 of the oscillator 200 isfed to the C (clock) terminal of the binary counter 211. The counter 211is generating a pulse signal as shown in (A) of FIG. 6 from its firststage output terminal Q₁. This pulse signal is coupled through theinverters 212 and 213 to the transistor 215 to drive this transistor.The output of the transistor is coupled through the terminal 104 to thefirst coil 15.

If the second coil 19 is displaced in the rightward direction withrespect to the first coil 15 as shown in FIG. 7A due to a rightwardtwist between the first and second rotors 11 and 16 shown in FIG. 2caused by a certain angle via the torsion spring 35, of the magneticflux generated by the first coil 15 that which crosses the second coil19 is increased. As a result, a voltage signal corresponding to theangle of twist as shown in (B) of FIG. 6 is generated in the coil 15 andsupplied to the capacitor 308 of the amplifier 300. A reference voltagefrom a voltage divider constituted by the resistors 302 and 303 isapplied through the resistors 304 to the other end of the capacitor 308and is coupled to the non-inverting input terminal of the operationalamplifier 301. Since the voltage from the voltage divider consisting ofthe resistors 302 and 303 is fed to its inverting input terminal, theinput signal to the capacitor 308, as shown in (B) of FIG. 6, isamplified by the operational amplifier 301. The output of theoperational amplifier 301 is shown in (C) of FIG. 6.

This amplified signal in (C) of FIG. 6 is coupled to the non-invertinginput terminal of the operational amplifier 453 of the left/rightdiscriminating circuit 450 for impedance conversion. The output of theoperational amplifier 453 is coupled through the resistor 458 to theinverting input terminal of the operational amplifier 454 for comparisonwith the voltage from the voltage divider consisting of the resistors459 and 460. Due to a response delay in the operational amplifier 454,the output signal is a pulse signal slightly delayed behind the inputsignal, and a signal as shown in (D) of FIG. 6 appears from the inverter455 and enters the D (data) terminals of the D-type filp-flops 451 and452.

Meanwhile, the pulse signal shown in (A) of FIG. 6 and an opposite phasepulse signal thereto are respectively supplied to the C (clock)terminals of the D-type flip-flops 452 and 451. Thus, the D-typeflip-flops 451 and 452 provide respective "0" and "1" level signals asshown in (E) and (F) of FIG. 6 from their Q output terminals.

The amplified output in (C) of FIG. 6 is also coupled to thenon-inverting input terminal of the operational amplifier 351 of thepeak hold circuit 350. Since the negative peak voltage of the amplifiedsignal is lower than the reference voltage from the voltage divider ofthe resistors 302 and 303, the negative peak voltage of the amplifiedsignal, as shown in (G) of FIG. 6, is provided as the hold output.

A pulse signal appearing from the 10-th output terminal Q₁₀ of thebinary counter 211 of the oscillator 200 is coupled through the resistor402 of the triangular wave generator 400 to the inverting input terminalof the operational amplifier 401. Due to the time constant of thecircuit consisting of the resistor 402 and capacitor 405, a triangularwave as shown in (H) of FIG. 6, is generated from the operationalamplifier 401. This output is coupled to the non-inverting inputterminal of the operational amplifier 501 in the pulse durationconverting circuit 500 for voltage ccmparison with a signal coupled tothe inverting input terminal as shown in (G) of FIG. 6. Thus a signal asshown in (I) of FIG. 6 is generated from the operational amplifier 501.This signal of (I) in FIG. 6 and also the signals of (E) and (F) in FIG.6 are coupled to the current value converting circuit 550. The NAND gate551 thus provides a "1" level signal as shown in (J) of FIG. 6 to turnon the transistor 555, thus causing current through the resistor 557.The inverter 553 provides an output signal as shown in (K) of FIG. 6 toon-off operate the transistor 556. Thus, necessary current is suppliedfrom the battery 51 through the constant voltage circuit 110, whereby apulse duration signal corresponding to the angle of twist of the torsionspring 35 is generated in the direction from a constant voltage leveltoward "0" level as shown in (L) of FIG. 6 at the end 53 of the currentdetecting resistor 52.

If the twist between the first and second rotors 11 and 16 in FIG. 2 viathe torsion spring 35 becomes zero, the second coil 19 is brought to thecenter of the first coil 15 as shown in FIG. 7B. In this state, themagnetic flux generated by the first coil 15 includes no componentvertically crossing the second coil 19. Thus, the voltage across thesecond coil 19 is reduced to "0" level as shown in the middle portion of(B) in FIG. 6.

Thus, the output of the amplifier 300 becomes equal to the referencevoltage of the voltage divider consisting of the resistors 302 and 303as shown in (C) of FIG. 6. With this voltage coupled to the left/rightdiscriminating circuit 450 and hold circuit 350, the output of theinverter 455 of the left/right discriminating circuit 450 is rendered tobe "0" level as shown in (D) of FIG. 6. As a result, the D-typeflip-flops 451 and 452 provide output of "0" level from their outputterminals Q as shown in (E) and (F) of FIG. 6. Also, the output voltageof the peak hold circuit 350 becomes equal to the reference voltage ofthe voltage divider of the resistors 302 and 303 as shown in (G) of FIG.6. The pulse duration converting circuit 500 thus provides an output of"0" level as shown in (I) of FIG. 6 to the current value convertingcircuit 550. Since the inputs to the NAND gates 551 and 552 are all at"0" level at this time, the output of the NAND gate 551 is thus renderedto be at "1" level as shown in (J) of FIG. 6, thus triggering thetransistor 555. Also, the output of the inverter 553 is rendered to beat "0" level as shown in (K) of FIG. 6, thus cutting off the transistor556. Thus, a constant voltage as shown in (L) of FIG. 6 is generated atthe end 53 of the current detecting resistor 52, indicating that thereis no twist in the torsion spring.

If the second coil 19 is leftwardly displaced with respect to the firstcoil 15 as shown in (C) of FIG. 7 due to a leftward twist between thefirst and second rotors 11 and 16 shown in FIG. 2 by a certain angle viathe torsion spring 35, portion of the magnetic flux generated by thefirst coil 15 that crosses the second coil 19 is increased. Since atthis time the direction of the magnetic flux crossing the second coil 19is opposite to that in the case of the rightward displacement. Thus, asignal of the opposite phase to that in case of the rightward twistbetween the first and seoond rotors 11 and 16 caused by the torsionspring 35 is generated in the coil 19 as shown in (B) of FIG. 6 (in theright hand end portion thereof). It will thus be seen that the sameoperation as in the case of the aforementioned rightward twist exceptthat the phase is opposite takes place (this being not described indetail). At this time, a pulse duration signal corresponding to theangle of twist of the torsion spring 35 is generated in the directionfrom the constant voltage level toward "1" level as shown in (L) of FIG.6 at the end 53 of the current detecting resistor 52.

While in the above embodiment the two rotors have beenelectromagnetically coupled together, it is also possible to use tworotors which are electrostatically coupled together.

FIGS. 8 to 14C show a second embodiment of the invention, whichincorporates two rotors electrostatically coupled together. In theFigures, like parts or corresponding parts to as those in the firstembodiment are designated by like reference numerals. FIG. 8 is afragmentary sectional view showing the internal construction of thesecond embodiment of the torque sensor 1. Designated at 11' is the firstrotor, to which a plate 64 having two kinds of first electrodes aresecured by screws as will be described hereinafter. Designated at 16' isthe second rotor, to which a second plate 68 having second electrodesare secured by screws as will be described hereinafter.

An electric circuit section 20' and a third plate having two ring-likeslip rings to be described later are bonded by an epoxy resin to thesecond rotor 16'. Brushes 24 and 25 are urged against the slip rings ofthe third plate 61 by brush holders 26 and 27 comprising spring membersso that they are electrically connected to the slip rings even when thesecond rotor 16' is rotating, and they are secured by screws to bedescribed later to connector pins 28 and 29. The connector pins 28 and29 are bonded by an epoxy resin to the connector holder 31. Theconnector holder 31 has a holder cover to be described later, which issecured by a screw to a housing 33 to be described later.

A torsion spring 35 is pressure fitted in the first and second rotors11' and 16' and secured thereto by the two knock pins 36. The first andsecond rotors 11' and 16' are coupled together via a bearing 37. Thesecond rotor 16' and housing 33 are coupled together via the bearing 38.The first and second rotors 11' and 16' which are coupled together bythe torsion spring 35, can thus be smoothly rotated with respect to thehousing 33.

FIG. 9 is a section of the torque sensor 1 taken along line IX--IX inFIG. 8. The illustrated construction shown in FIG. 9 is approximatelythe same as that of FIG. 3 except that the second rotor 16' instead ofthe first rotor 11 in FIG. 3 is shown with the third plate 61.

FIG. 10 is a sectional view of the torque sensor taken along line X--Xin FIG. 8. In the Figure, designated at 16' is the second rotor, towhich the second plate 68 is secured by the screw 69. Designated at 64is the first plate as mentioned above, which is secured by the screw 65to the first rotor. A portion 39 of the second rotor 16' serves as astopper for preventing the displacement of the first and second rotorsrelative to each other beyond a predetermined angle. FIG. 11 is a planview showing the second plate 68 shown in FIG. 8. It has a secondelectrode 67 having a portion 70 connected to the electric circuit 20'mentioned above. FIG. 12 is a plan view showing the first plate 64 shownin FIG. 8. It has two kinds of comb electrodes 71 and 73 and therespective kind of electrodes are connected to each other. Theseelectrodes 71 and 73 are connected through respective terminals 75 and77 to the electric circuit 20'.

FIG. 13 is an electric circuit diagram for the second embodixent of thetorque sensor according to the invention, and voltage waveformsappearing at various parts of the circuitry are such as shown in (A) to(L) of FIG. 6. Namely the construction and operation of the circuitry ofFIG. 13 are the same as those having been shown and described inconnection with FIG. 5 except that the coupling relation amongoscillator 200', input terminals 103' to 105', detecting electrodes 67,71 and 73, triangular wave generator 400 and left/right discriminatingcircuit 450 is different from one in the circuitry of FIG. 5. Now, partof the circuitry of FIG. 13 that is different from one in the circuitryof FIG. 5 will be described.

Referring to FIG. 13, a terminal 103' is connected through the portion70 of the second plate 68 to the comb-shaped second electrode 67.Terminals 104' and 105' are connected through portions 75 and 77 of thefirst plate 64 to the comb-shaped first electrodes 71 and 73 shown inFIG. 12.

An oscillator 200', which includes an oscillating circuit havinginverters 201 and 202, a ceramic oscillator 203, a resistor 204 andcapacitors 205 and 206, a binary counter 211 and inverters 212, 213 and214 in the illustrated connection, generates opposite phase rectangularwaves (e.g., one phase wave as shown in (A) of FIG. 6) which arerespectively supplied through the terminals 104' and 105' to the firstelectrodes 71 and 73.

The left/right discriminating circuit 450 discriminates whether adisplacement of the second electrode 67 is toward either the firstelectrode 71 or 73. The current value converting circuit 550 convertssignals produced from the left/right discriminating circuit 450 andpulse duration converting circuit 500 into corresponding current valuechanges. That is, this circuit transmits information about the extent ofoverlap of the second electrode 67 over either first electrode 71 or 73,in the form of current value changes, to the power supply terminal 101.This information is detected as voltage changes at one end 53 of theresistor 52.

The operation of the construction described above will now be describedwith reference to (A) to (L) of FIG. 6. A pulse signal generated fromthe inverter 202 of the oscillator 200' is fed to the C (clock) terminalof the binary counter 211, and a pulse signal as shown in (A) of FIG. 6is being supplied through the terminal 105' to the first electrode 73. Apulse signal of the opposite phase to the signal of (A) of FIG. 6 isbeing supplied from the inverters 213 and 214 through the terminal 104'to the first electrode 71.

If the second electrode 67 is displaced toward the first electrode 71 asshown in FIG. 14A due to a rightward twist between the first and secondrotors 11' and 16' shown in FIG. 8 caused by a certain angle via thetorsion spring 35, the overlap area of the second electrode 67 and firstelectrode 71 is increased. As a result, the electrostatic capacitancebetween these electrodes becomes larger than the electrostaticcapacitance between the second electrode 67 and first electrode 73,whereby a voltage signal corresponding to the twist angle as shown in(B) of FIG. 6 is produced from the second electrode 67 and fed to thecapacitor 308 of the amplifier 300.

Meanwhile, the reference voltage from the voltage divider comprised ofthe resistors 302 and 303 is applied to the other end of the capacitor308 and is coupled to the non-inverting input terminal of theoperational amplifier 301. Since the voltage from the voltage dividercomprised of the resistors 302 and 303 is coupled to its inverting inputterminal, the operational amplifier 301 amplifies the signal coupled tothe capacitor 308 shown in (B) of FIG. 6. The amplified output such asshown (C) of FIG. 6 is applied to the non-inverting input terminal ofthe operational amplifier 453 and the subsequent circuit stages effectthe similar operation to that of the circuit shown in FIG. 5. Thus thesignals such as shown in (D) to (L) of FIG. 6 are generated by therespective circuits, and the pulse signal of (L) of FIG. 6 which has apulse width corresponding to the twist angle of the torsion spring 35 isgenerated toward "0" level from a certain voltage level.

If the twist between the first and second rotors 11' and 16' in FIG. 8via the torsion spring 35 becomes zero, the second electrode 67 isbrought to a position mid way between the first electrodes 71 and 73 asshown in FIG. 14B. In this state, the electrostatic capacitance betweenthe second electrode 67 and first electrode 71 is equal to theelectrostatic capacitance between the second electrode 67 and firstelectrode 73. Thus, the voltage at the second electrode 67 is renderedto be "0" level as shown in (B) of FIG. 6. Also, the output voltage ofthe amplifier 300 becomes equal as shown in (C) of FIG. 6 to thereference voltage of the voltage divider comprised of the resistors 302and 303. This voltage is supplied to the left/right discriminatingcircuit 450 and peak hold circuit 350. Similar to the circuit operationin FIG. 5 the signals of intermediate portions shown in (D) to (L) ofFIG. 6 are subsequently generated, and the signal of (L) of FIG. 6indicates that no twist occurs in the spring 35.

If the second electrode 67 is displaced toward the first electrode 73 asshown in FIG. 14C due to a leftward twist between the first and secondrotors 11' and 16' in FIG. 8 caused by a certain angle via the torsionspring 35, the overlap area of the second electrode 67 and firstelectrode 73 is increased. As a result, the electrostatic capacitancebetween these electrodes becomes larger than the electrostaticcapacitance between the second electrode 67 and first electrode 71.Thus, a signal of the opposite phase to that in case of the rightwardtwist between the first and second rotors 11' and 16' in FIG. 8 causedvia the torsion spring 35 is generated from the second electrode 67 asshown in the right portion of (B) of FIG. 6. It will thus be seen thatthe same operation as in the case of the afore-mentioned rightward twistexcept that the phase is opposite takes place (therefore this is notdescribed in detail). Thus, a pulse duration signal corresponding to theangle of twist of the torsion spring 35 is generated, in the directionfrom the constant voltage level toward " 1" level as shown in (L) ofFIG. 6, at the end 53 of the current detecting resistor 52.

While the above two embodiments have used a ceramic oscillator elementfor providing oscillation in the oscillator 200 or 200', the sameeffects may also be obtained by using an RC oscillating circuit or acrystal oscillator element. Also, while the negative peak voltage hasbeen detected in the peak hold circuit 350, it is also possible todetect the positive peak voltage.

Further, while a triangular wave has been generated using the triangularwave generating circuit 400 for obtaining a pulse signal proportional tothe voltage generated in the peak hold circuit 350, it is also possibleto use a sawtooth wave. Further, while in the first embodiment a pulsevoltage signal is impressed upon the first coil, it is possible toimpress a sinusoidal wave.

As has been described in the foregoing, according to the inventionchanges in the state of electromagnetic or electrostatic couplingbetween two rotors, which are rotatable relative to each other bydetected torque via a torsion bar, are detected for detecting torque, itis possible to provide a torque sensor, which can preclude the drawbacksinherent in the prior art torque sensor suing a semiconductor straingauge, which is very beneficial in the relevant fields.

I claim:
 1. A torque sensor comprising:a first rotor having two kinds offirst electrodes; a second rotor having a second electrode, said secondelectrode facing said two kinds of first electrodes at a predetermineddistance therefrom and coupled thereto electrically by electrostaticcapacitance coupling and mechanically by a torsion spring; and anelectric processing circuit for impressing electric signals of oppositephases to said respective kinds of first electrodes and generating asignal corresponding to the magnitude of twist of said torsion springfrom a signal generated from said second electrode according to themagnitude of electrostatic capacitance corresponding to the overlap areaof one kind of said first electrodes and said second electrode, saidoverlap area being variable with the rotation of both said rotorsrelative to each other caused by said torsion spring, wherein each kindof said first electrodes are comb-shaped electrodes connected to eachother and said second electrode is a comb-shaped electrode the pitch ofwhich is double the pitch of said comb-shaped first electrodes.
 2. Atorque sensor comprising:a first rotor having two kinds of firstelectrodes; a second rotor having a second electrode, said secondelectrode facing said two kinds of first electrodes at a predetermineddistance therefrom and coupled thereto electrically by electrostaticcapacitance coupling and mechanically by a torsion spring; and anelectric processing circuit for impressing electric signals of oppositephases to said respective kinds of first electrodes and generating asignal corresponding to the magnitude of twist of said torsion springfrom a signal generated from said second electrode according to themagnitude of electrostatic capacitance coresponding to the overlap areaof one kind of said first electrodes and said second electrode, saidoverlap area being variable with the rotation of both said rotorsrelative to each other caused by said torsion spring, wherein saidelectric processing circuit includes: an oscillating circuit oscillatingat a constant frequency to impress electric signals of opposite phasesto said two kinds of first electrodes; an amplifying circuit foramplifying a signal generated from said second electrode; adiscriminating circuit for discriminating the direction of twist of saidtorsion spring by comparing signals from said amplifying circuit andfrom said oscillating circuit; and a peak hold circuit for detecting thepeak of the output voltage from said amplifying circuit and generating adirect current voltage corresponding to the magnitude of twist of saidtorsion spring.
 3. A torque sensor comprising:a first rotor having twokinds of first electrodes; a second rotor having a second electrode,said second electrode facing said two kinds of first electrodes at apredetermined distance therefrom and coupled thereto electrically byelectrostatic capacitance coupling and mechanically by a torsion spring;and an electric processing circuit for impressing electric signals ofopposite phases to said respective kinds of first electrodes andgenerating a signal corresponding to the magnitude of twist of saidtorsion spring from a signal generated from said second electrodeaccording to the magnitude of electrostatic capacitance corresponding tothe overlap area of one kind of said first electrodes and said secondelectrode, said overlap area being variable with the rotation of bothsaid rotors relative to each other caused by said torsion spring,wherein said oscillating circuit impresses signals of opposite phasesone upon one of said two kinds of first electrodes through an inverterand the other upon the other of said first electrodes through twoinverters.
 4. In a power assisted steering apparatus having torqueassisting motor means coupled to a steering main shaft, the torquesensor according to either claim 1 or 3, which further comprises;meansfor causing the rotation of one of said first and second rotorsaccording to torque generated in said main shaft; and means for drivingsaid motor according to the output signal of said electric processingcircuit.
 5. A torque sensor comprising:a first rotor having two kinds offirst electrodes; a second rotor having a second electrode, said secondelectrode facing said two kinds of first electrodes at a predetermineddistance therefrom and coupled thereto electrically by electrostaticcapacitance coupling and mechanically by a torsion spring; and anelectric processing circuit for impressing electric signals of oppositephases to said respective kinds of first electrodes and generating asignal corresponding to the magnitude of twist of said torsion springfrom a signal generated from said second electrode according to themagnitude of electrostatic capacitance corresponding to the overlap areaof one kind of said first electrodes and said second electrode, saidoverlap area being variable with the rotation of both said rotorsrelative to each other caused by said torsion spring, wherein saidelectric processing circuit includes: a triangular wave generatedcircuit for generating a triangular wave at a constant frequency fromthe signal from said oscillating circuit; a pulse duration detectingcircuit for generating a signal having a pulse duration proportional toa direct current voltage corresponding to the magnitude of twist of saidtorsion spring from signals from said triangular wave generator and fromsaid peak hold circuit; and a current converting circuit for generatinga current signal, said current signal having one of three current levelscorresponding to signals from said left/right discriminating circuitrespectively representing leftward twist, no twist and rightward twistof said torsion spring, said current signal having a durationcorresponding to a signal from said pulse duration detecting circuitrepresenting the magnitude of twist of said torsion spring; the outputsignal of said torque sensor being superimposed upon a power sourceline.
 6. The torque sensor according to claim 5, which furthercomprises;means for connecting a power source and ground through brushesto slip rings; and means for permitting free rotation of said first andsecond rotors with respect to said housing.